Skip to main content

Adaptive mechanisms of ecological divergence in sibling allopolyploid lineages

Final Report Summary - POLYADAPTATION (Adaptive mechanisms of ecological divergence in sibling allopolyploid lineages)

Hybridization and whole genome doubling (WGD, or polyploidization) have been central to the evolution of flowering plants, starting with their origin. Immediately following a WGD and/or a hybridization event, a genome suffers adjustments in organization and function at the genetic and epigenetic level, thereby shaping the adaptive success and the evolutionary fate of resulting lineages. The PolyAdaptation project was part of a larger research plan that uses ecologically-divergent, sibling Dactylorhiza allopolyploids of different ages to investigate how iterative genome merger events (i.e. allopolyploidy) can generate functional diversity, thereby contributing to rapid adaptation and evolutionary diversification.
A first step of this research was to define genetically the lineages present in this group and to investigate the processes that allow them to remain distinct while sharing the same genetic heritage and ploidy. By analysing ca. one million genome-wide nucleotide positions we document a genome-wide absence of genetic differentiation between these allopolyploid lineages despite the visible phenotypic divergence. Based on this large scale data, we obtain a (weak) geographic signal, identifying three genetic clusters made up of i) British accessions of D. traunsteineri and D. ebudensis, ii) Scandinavian plus some of the Alpine accessions of D. traunsteineri, and iii) the rest of D. majalis and D. traunsteineri individuals. Our data demonstrate that when geographic barriers are absent or weak an asymmetrical gene flow between the polyploids is frequent, with genes of D. majalis slowly introgressing into D. traunsteineri, thereby opposing genetic differentiation. Such a conclusion is also consistent with the weaker morphological differentiation between D. majalis and D. traunsteineri observed in the Alps. More details are available at http://www.botanik.univie.ac.at/systematik/projects/dactylorhiza/research_4.html and http://www.botanik.univie.ac.at/systematik/projects/dactylorhiza/research_5.html.
With funds from outside the flat-rate contribution of PolyAdaptation, we have also investigated gene expression alterations triggered by the recurrent WGD with the aim to better understand their importance to the ecological properties of polyploids. For this aim we quantitavely sequenced the expressed genes across 29 individuals, including representatives of the three polyploids and the two diploid parents. We observe a trend of increased overexpression of genes in the younger D. traunsteineri in comparison to D. majalis, whose transcriptome generally resembles more closely those of the diploid parents. Significantly overexpressed genes in D. traunsteineri as compared to D. majalis include some of ecological relevance. More details and updates can be found at http://www.botanik.univie.ac.at/systematik/projects/dactylorhiza/research_6.html.
During the PolyAdaptation funding period the fellow set up a group of Plant Ecological Genomics at the University of Vienna (http://plantgenomics.univie.ac.at) within the Department of Botany and Biodiversity Research. The group is currently formed by one postdoc, three PhD students, one MSc student, one technical assistant and the group leader. The group is mainly funded from a 6 years grant associated with a prestigious START award obtained by the fellow in 2013. During the PolyAdaptation funding period the fellow has also been invited to join as faculty a doctoral school in Vienna, and as associate editor the board of the Botanical Journal of the Linnean Society of London. The fellow has organised during the PolyAdaptation grant period two symposia on Evolutionary Epigenetics at international conferences (at the XVIII International Botanical Congress, Melbourne, Australia, 2011 and at the BioSystEU2013, Vienna, Austria, 2013).